Sequence of electric and gas operation in water heater

[howardwheeler]

I have a suburban 10 gallon gas and electric hot water heater. I just discovered my electric element burnt out, and in fixing it a question arose in my mind. I like to have both heat sources on so recovery is faster, but I realized my electric element was out because I began to notice how often my propane burner was burning. What I want of course is for the electric element to do all the regular maintaining of the temperature and for the propane to kick in only when water is being used in a large amount. I don't want to unnecessarily drain my propane tanks. And it seems that's what my water heater does, because I only noticed the propane on a lot when my electric element burnt out. Is it true then that when the thermostat calls for the water to be heated a little bit that first the electric element comes on? Does the propane not kick in unless there is a higher demand? Or does a drop in water temperature cause the thermostat to just kick on both the element and the burner? Is ther a sequence designed into the system? Or do I have to turn the propane off to make sure that anytime the water temp falls a little that only the electric element will maintain temperature?

[Old-Biscuit]

The pre-set t-stats 'close' when temp cools and 'open' at a pre-set temp

Suburban uses a 'standard' 130*F t-stat and a 180*F ECO (high temp) t-stat
They come in a set. One set for electric & one set for gas. The electric is a 120V AC set and the gas is a 12V DC set.

When the 'normal' t-stat opens (130*F) the water temp (tank wall where t-stat is held tight against with a nut) has to cool off enough for the t-stat to close....roughly 110*F

If you have different ranges of t-stats the lower temp t-stat will do all the heating cause the higher temp t-stat will not cool off enough to close.

If the ECO t-stat opens it cuts off all power for that function (electric or gas) and has to be reset (the reset is under rubber cover which protects t-stats from exposure to elements and keeps them from cooling off from outside air vs tank wall temp)

Atwood uses a standard 140*F & 180*F t-stats.......since 2004 just one set for electric & gas so if problem with t-stat nothing works and if ECO opens you can't reset it..you have to wait until temp cools enough for it to close. They do have an adjustable t-stat to replace pre-set 140*F t-stat.

Simple designs....not 'smart' enough for selective heating

[richardcoxid]

Here is a hint when using Gas/Elect simultaneously.

The water temperature when using either Gas or Elect in most models of RV HWHs is controlled by non-adjustable (either on or off) Snap Stats. These are small thermostats about 1/2in in Dia and about 3/8in high exclusive of the push on connector terminals. On a typical RV HWH they are held in contact with the metal tank with a small (about 2in x 2in) piece of black foam tape. Normally the Gas stat will be on the gas burner side of the HWH and the elect stat on the elect heating element side of the HWH.

Carefully remove the tape and record the part numbers of the Gas “stat”. A wholesale electrical supplier or others should be able to cross-reference the “on” temperatures of each. Chose a new “GAS “stat (it’s a small dollar item) that turns “ON” about 10 degrees lower than the elect stat.

Now, when both Gas and Elect are turned “ON” , a small usage of hot water or normal heat loss will cause the elect stat to turn “ON” first (use the CG’s electricity not my propane). If the bulk temp. of the water continues to decrease then the Gas stat will turn “ON” for a very fast recovery time.

May you have fair winds and following seas!

Disclaimer- BE SAFE!- Be sure to de-energize the 120 VAC and the 12VDC before working on the HWH!

[wa8yxm]

A lot depends on the design of the heater.. Folks are saying Surburan uses one T-Stat for 120 and one for gas. So if you get a 130 for Electric (A bit hotter than normal) and a 120 for gas, Gas should only kick in when needed.

My attwood has two thermostats as well.. ONE for 120 and one for, I think 180,190 or 200 (Emergency cut out) you don't want that one operating ever.

Ini short, on my unit both gas and electric,, Same T-stat..

And just now.. Gas is non-op (Control failure) YES, I know what is needed to replace it and thanks for the reminder.

[RVUSA]

I use the electric all the time and when I shower I flip on the gas as well. It helps to keep the water hot longer.

I am really surprised in the hot time difference between a 10 gl. attwood and a 10 gl.suburban. The atwood when supplemented with the gas heat never ran out of hot water with 2 people showering consecutively. With this rv the suburban runs out of hot within the first shower.

[howardwheeler]

BB TX, your experience matches my own. Maybe there are two different temperature settings for the different thermostats. It does make sense to let the electric do the majority of the work.

[doxiemom11]

We have a 10 gallon. We keep it on electric all the time and do not even use the gas. We have never run out of hot water. If we wanted to shower one right after the other we could turn on the gas, but we just wait 15 min or so in between and have no problem using just the electric. Just keep your gas switch "off" unless you want it, then flip it on. Shut back off when you are done needing it.

[BB_TX]

I almost always run my Surburban on both electric and gas at the same time for fast recovery when taking showers.
Don't know what my thermostats are set for but the gas almost never turns on unless we are using hot water for showers or clothes washer.
If the electric is not on, then I often hear the gas kick on to reheat the water, especially if the weather is cool. Annoying at night.

[Chris_Bryant]

There are 2 thermostats, but they are rarely the same temperature. Most often the electric thermostat is set at 120° F and the LP at 130°, but you can buy a 140° for the electric (p/n 232317).

[howardwheeler]

It's not the cost but the fact that I have to go get the bottles filled and if it's cold enough it shortens my furnace capacity. When plugged into the campground it just seems better. I just began to wonder and came to the conclusion that a staged set of thermostats would have been a good engineered setup. It would only take a few degree differential, but it seems from what folks have said, it's not the case. Too bad.

[aruba5er]

Who is paying the electric bill. If you than propane is about 3 times cheaper. If included in your camp fee, the go with electric or both. Thermos are not adjustable so really either one could start or run first. Forget about it and enjoy camping. Don"t sweat the small stuff.

[j-d]

I don't believe there is ANY relationship between LPG and 120VAC. You select Either Neither or Both and it does what it can do. Including running both till one t'stat is satisfied, then the other.

It seems from what you say that the LPG thermostat is set (translation: Built - Don't think they're adjustable) higher than your electric t'stat. AFIK the "standing pilot" LPG heaters use an adjustable t'stat but the DSI types do not. Also, none of the OEM electric t'stats seem to be adjustable. If you want LPG "backup" for your 120VAC operation I think you'll have to turn it on yourself.

Our coach is 30A, and we often find we can't run our 15K A/C and the WH on Electric in the summer. I've found that the DSI LPG feature provides hot water so quickly, that not having a full hot tank from 120VAC operation isn't really a problem. I can turn the WH on partway through a meal and have plenty of HOT water for dishes. 10-minutes or so.

[cpaulsen]

On my Suburban 10 gallon WH...I always run on 110 when I can....the very few times I have needed more hot water...I just turn the propane on and it runs for a very short time then shuts off and the electric keeps the temps up.I very rarely use the propane with the 10 gallon WH. Never have run out of hot water on electric even with a 15-20 minute shower.

[Old-Biscuit]

Two completely different sets of T-stats...but both are pre-set the same

One 120V AC set (normal and ECO) for electric element
One 12V DC set (normal and ECO) for propane

Both normals are pre-set for 130F (turn off temp) and both ECO (high temp) are pre-set for 170*F (turn off temp)

You can get a lower pre-set......120*F
Or a higher pre-set.....140*F

Higher pre-set for electric.......both propane/electric would come on. Propane would shutoff at 130*F and electric would continue operating until 140*F

DISCLAIMER:
Not sure of temp that t-stats close at. (Typically 30*F spread from close to open)
If the same open/close range for t-stats then the higher pre-set t-stat would close 10*F before the other and open 10*F higher than other.
Soooo propane may not come on at all when using electric & propane with different temp t-stats due to the same open/close range?????

Probably easier to run both until water is heated then turn propane off and let electric maintain. Then kick propane back on for fast recovery.....if needed.
We use electric only when we have AC power and save the propane for when we don't have AC power